1. Field of the Invention
This invention relates to an improved magneto-type D-C electric motor.
2. Prior Art
A conventional motor of this type is shown in FIG. 1, in which reference numeral 1 denotes a magneto-type D-C electric motor, and reference numeral 2 denotes a field device which consists of a cylindrical yoke 3 made of a soft steel plate and a permanent magnet 4 adhered to the inner peripheral surface of the yoke with an adhesive agent. Reference numeral 5 denotes a rear bracket fastened to a socket portion 3a which is formed in an end surface of the yoke 3, reference numeral 6 denotes a brush device secured to the rear bracket, reference numeral 7 denotes a brush for supplying electric power, reference numeral 8 denotes a brush holder for slidably holding the brush, reference numeral 9 denotes an insulation plate which is secured together with the brush holder as a unitary structure, and reference numeral 10 denotes a base plate secured to the rear bracket 5. Reference numeral 11 denotes a sleeve bearing fitted to a protruded portion 5a of the rear bracket 5, reference numeral 12 denotes an armature which is supported by the rear bracket via the sleeve bearing 11 in a manner to be opposed to the permanent magnet 4 maintaining a small gap in the radial direction, reference numeral 13 denotes a rotary shaft of the armature, and reference numeral 14 denotes a commutator fitted to a rear portion of the rotary shaft 13. The brush 7 is brought into slidable contact with the commutator 14. Reference numeral 16 denotes an armature core on which are wound armature coils, reference numeral 17 denotes a thrust washer, and 18 denotes a stopper.
Operation of the thus constructed conventional motor will be described below.
When power-source device (not shown) is connected to the brushes 7, the armature 12 is served with electric power via commutator 14 and is energized. Namely, the armature 12 rotates since it is urged by the permanent magnet 4. A reactive rotational force is developed in the permanent magnet 4, and is transmitted to the yoke 3 via the layer of adhesive agent.
In the conventional device as mentioned above, the permanent magnet 4 constituting the field poles, and the brush holder 8 are separately positioned in the circumferential direction. Therefore, it is difficult to accurately place the brush holder and the field poles at predetermined positions relative to one another. Namely, error develops with regard to positions for mounting the brush holder and the field poles during the assembling steps, causing the electric characteristics of the motor to become deteriorated.